need help on screen shot

after uploading screenshot of file,instead of displaying screenshot of file while viewing the file the following error is displayed:
"Warning: imagecreatefrompng()
[function.imagecreatefrompng]: '../download/screen/Quran-
english.jar.png' is not a valid
PNG file in /home/ u632246788/public_html/
download/view.php on line 203 Warning: imagecolorallocate(): supplied argument is not a
valid Image resource in / home/u632246788/public_
html/download/view.php on line 206 Warning: imagecopyresized(): supplied argument is not a
valid Image resource in / home/u632246788/public_
html/download/view.php on line 220 Warning: imagepng() [function.imagepng]: gd-png: fatal libpng error: zlib error in /home/u632246788/
public_html/download/
view.php on line 244 Warning: imagepng() [function.imagepng]: gd-png error: setjmp returns error
condition in /home/ u632246788/public_html/
download/view.php on line 244 Warning: imagedestroy(): supplied argument is not a
valid Image resource in / home/u632246788/public_
html/download/view.php on line 248"

ok, thanks